Prader–Willi Syndrome (PWS)

Prader–Willi syndrome (PWS) is a rare genetic disorder caused by the loss of function of specific genes on chromosome 15, typically due to a paternal deletion or maternal uniparental disomy (UPD 15). It manifests with a range of symptoms, including weak muscles and poor feeding in infants, and constant hunger, intellectual impairment, and behavioural problems in children. This disorder affects approximately 1 in 10,000 to 30,000 people worldwide.

Signs and Symptoms

PWS symptoms vary with age. In infants, it is characterised by poor muscle tone (hypotonia), weak sucking reflex, and developmental delays. Other signs include lack of eye coordination, almond-shaped eyes, a thin upper lip, and weak crying. As children grow, they exhibit excessive sleeping, delayed milestones, strabismus, scoliosis, cryptorchidism, speech delay, poor physical coordination, and hyperphagia (excessive hunger), which starts between the ages of 2 and 8 and persists into adulthood. This compulsive eating often leads to obesity and related complications, such as type 2 diabetes.

Adults with PWS tend to have infertility, continued hypotonia, learning disabilities, and extreme flexibility. Characteristic physical features include a high, narrow forehead, thin upper lip, downturned mouth, almond-shaped eyes, small hands and feet, soft and easily bruised skin, and a lack of complete sexual development. Conditions like hypogonadism, sparse pubic hair, and a tendency towards type 2 diabetes mellitus are common.

Neurocognitive and Behavioural Aspects

Individuals with PWS often display learning and attention difficulties. They typically have stronger skills in visual organisation and perception, including reading and vocabulary, but weaker spoken language abilities, arithmetic, writing skills, and memory. Behaviourally, PWS is associated with a relentless appetite, necessitating strict food supervision to prevent morbid obesity. Patients may exhibit compulsive behaviours, such as skin picking, and psychiatric symptoms, including hallucinations, paranoia, and depression. They are often extremely stubborn and prone to temper tantrums.

Genetics

PWS results from an epigenetic phenomenon called imprinting. Normally, a foetus inherits an imprinted maternal copy and a functional paternal copy of certain genes on chromosome 15. In PWS, there is a mutation or deletion of the paternal copies, leading to a lack of functional PW genes. The genes involved include SNRPN, NDN, and clusters of snoRNAs like SNORD64, SNORD107, SNORD108, SNORD116, and SNORD115. The same chromosomal region is implicated in Angelman syndrome (AS), which occurs due to maternal gene defects.

Diagnosis

PWS is diagnosed through genetic testing, especially DNA-based methylation testing, which detects the absence of the paternally contributed PWS/AS region on chromosome 15q11-q13. Early diagnosis is very important for timely intervention, including growth hormone therapy, which supports growth and muscle mass, and may reduce food preoccupation.

Treatment

While there is no cure for PWS, several treatments can mitigate its symptoms. Infants may benefit from therapies to improve muscle strength, and speech and occupational therapy. To manage obesity, strict supervision of food access is necessary, often requiring locks on food storage areas. Physical activity is essential to maintain strength and health. Daily recombinant growth hormone injections are recommended for children, supporting growth and muscle development.

Behavioural and psychiatric issues are best managed with parental education, training, and, in some cases, medication. Serotonin agonists can help manage temper tantrums and compulsive behaviours. Obstructive sleep apnoea, common due to obesity, may require positive airway pressure therapy. Surgical interventions, like gastric bypass, have generally been unsuccessful in treating obesity.

Epidemiology

PWS affects approximately 1 in 10,000 to 1 in 25,000 newborns, with over 400,000 people living with the condition globally.

Society and Culture

PWS has been depicted in popular culture, often due to the curiosity around its symptoms. Notable individuals include Katie Price's son Harvey. The syndrome has also featured in various television shows and documentaries, such as CSI: Crime Scene Investigation, Can't Stop Eating, and Extreme Makeover: Home Edition.

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Self-assessment MCQs (single best answer)

What is the primary genetic cause of Prader-Willi Syndrome (PWS)?

Which of the following symptoms is characteristic of infants with PWS?

At what age does hyperphagia typically begin in children with PWS?

Which gene cluster is involved in Prader-Willi Syndrome?

What type of genetic testing is primarily used to diagnose PWS?

Which of the following physical features is NOT typically associated with PWS?

What is the recommended treatment to support growth and muscle development in children with PWS?

Which behavioural characteristic is commonly seen in individuals with PWS?

What is a common medical complication in adults with PWS due to obesity?

Which historical figure is presumed to have had PWS, as depicted in a painting by Juan Carreño de Miranda?